This invention relates generally to domestic electric baking ovens. In a conventional oven, during the baking process, a thermostat switches a single high wattage element, located in the bottom of the oven, on and off to provide an average air temperature that has been preselected. Temperatures vary from 15.degree.-30.degree. C. on either side of the selected average air temperature. Element surface temperatures have been measured at 800.degree. C. although the foods that are typically cooked in an oven are done at internal temperatures of 100.degree. C. or below. Since the element is located at the bottom of the oven cavity a large amount of infrared radiation is directed toward the lower surface of a product or utensil in the oven thus resulting in the baking of food products from bottom to top.
The portions of the food that are exposed to the upper areas of the oven cavity are heated by convection as air circulates to the food after passing the hot element or by infrared radiation that has been absorbed by the oven cavity walls and top and is reradiated to the food. To function properly, the conventional oven requires use of an element rated at 2000-3000 watts. Thus, the cumbersome process of radiating, absorbing, reradiating and convecting heat results in unnecessarily high energy usage and longer than necessary baking times. The conventional system also requires a higher radiant element surface temperature to accomplish radiant heating of the cavity walls which in turn causes convective heating of air within the oven cavity.
In the conventional baking system, the vaporization of moisture at the upper surfaces of the food keeps those surfaces of the food cool and slows the cooking process in the food from the top down. To keep the lower surfaces of the food, the portions in contact with the pan, from overcooking and burning before the upper portions can get done, pans must be designed to reflect much of the infrared radiation presented to the bottom of the pan. For example, in cake pans recommended for electric ovens, the emissivity E is about 0.077 for a pan bottom and 0.05 for a pan side. Emissivity E is also equal to absorptivity of radiant energy. The pan side absorbs radiation a little less readily than the bottom to discourage overcooking of the edges of the food.
Preheating is important in the conventional electric oven system for many heat sensitive foods because it allows oven walls to absorb infrared radiation and become part of the cooking system by reradiating power to the upper portion of the product when it is placed in the oven to bake. Without preheating, oven walls absorb infrared radiation and become part of the cooking system later in the baking process. Conventional range ovens are patterned after older and less efficient range ovens in wood and coal stoves that were developed to harness the heat from unwieldy flames. Electric ovens were developed 60-70 years ago and their design has never been reviewed in light of the function they perform or the sophisticated and easily controlled energy source used.
Heretofore, various food heating and reheating systems using plural radiant sources have been designed as disclosed in U.S. Pat. Nos. 3,131,280 to Brussell; 3,414,709 to Tricault; 3,626,155 to Joeckel; 3,682,643 to Foster; and 3,820,525 to Pond. In order to accomplish the baking process, these systems provide for some combination of heating modes including conduction to the pan, forced or free convection to the pan and/or multiple products, and radiant power from high temperature sources. However, none of these systems have solved the problem of effectively coupling low temperature radiant heat sources to food products to thereby reduce heating time and energy consumption.